This invention relates to a nitride-based semiconductor light emitting element using a translucent electrode as an electrode of a nitride-based semiconductor represented by InXAlYGa1-X-YN (0≦X, 0≦Y, X+Y<1).
There are two types of light emitting element as a light emitting element having a nitride-based semiconductor layer on an insulate growth substrate such as sapphire (Al2O3) substrate: the one is a face-up type light emitting element which is mounted on a mounting part of a printed substrate at the sapphire substrate side, and the other one is a face-down type light emitting element which is mounted on a mounting part of a printed substrate at the nitride-based semiconductor side. In the former one, as the light extracting surface of the main light emitting element is upper-surface of the nitride-based semiconductor side, the electrode formed on the top have to be a translucent electrode.
In general, the face-up light emitting element that uses ITO (Indium-Tin-Oxide) as a translucent electrode is well known.
The nitride-based semiconductor has a high refractive index of about 2.5. Therefore, in the case of using the nitride semiconductor as the light emitting element, it is required to improve light extraction efficiency of the light emitting element by increasing a critical angle of an interface by reducing a refractive index difference between the translucent electrode and the nitride-based semiconductor.
Since ITO has a refractive index of 1.8 to 1.9, a translucent electrode having a higher refractive index is in demand. As one example the translucent electrode, the use of ICO (Indium-Cerium-Oxide) having a refractive index of 2.0 to 2.1 is considered (see JP-A-2006-279005, for example).
However, ICO has large sheet resistance and a high forward voltage (VF) due to its unsatisfactory current diffusion property. Due to such properties, there has been a problem of poor light emission efficiency of the light emitting element.